Chapter 4: Control Charts for Variables in Statistical Process Control
Abstract: Control charts for variables in Statistical Process Control (SPC) monitor measurable characteristics (like weight, height, diameter) using paired charts: an X-bar (mean) chart tracks the process average (centering) and an R (range) chart or S (standard deviation) chart tracks variability (spread) . These charts use Upper and Lower Control Limits (UCL/LCL) based on sample data to distinguish between normal process variation and significant shifts, helping identify issues like poor materials or machine problems. Key Types of Variable Control Charts X-bar (Mean) Chart : Plots the average of subgroups over time to check if the process is centered correctly. R (Range) Chart : Plots the range (max - min) within subgroups to monitor process spread (variability). S (Standard Deviation) Chart : Also monitors variability, often preferred for larger sample sizes over R charts. Individual & Moving Range (I-MR) Charts : Used for single observat...